I'm in high school and I'm quite new to set theory. Off and on I've been surfing Wikipedia and other wikis to learn more about set theory, and right now I am working through a book called "A Book on Set Theory" by Charles C. Pinter, republished by Dover publications.
Basically, what I need is a thick book to go to next to study deeper into set theory. To add, I'm not at all afraid about writing page-long proofs as answers to exercise questions.